(1R,2R,3S,6aS,7R,8R,9S,12aS)-1,2,3,7,8,9-Hexahydroxyperhydrodipyrido[1,2-a:1′,2′-d]pyrazine-6,12-dione

The crystal structure of the title compound, C12H18N2O8, exists as O—H⋯O hydrogen-bonded layers of molecules running parallel to the ab plane. Each molecule is a donor and acceptor for six hydrogen bonds. The absolute stereochemistry was determined by the use of d-glucuronolactone as the starting material.

The crystal structure of the title compound, C 12 H 18 N 2 O 8 , exists as O-HÁ Á ÁO hydrogen-bonded layers of molecules running parallel to the ab plane. Each molecule is a donor and acceptor for six hydrogen bonds. The absolute stereochemistry was determined by the use of d-glucuronolactone as the starting material.
We would like to thank the Chemical Crystallography department and ALT at the University of Oxford for use of the diffractometers.

Experimental
The title compound was recrystallised by diffusion from a mixture of water and acetonitrile: m.p. 511 K decomposed; [α] D 20 + 29.7 (c, 0.35 in H 2 O).

Refinement
In the absence of significant anomalous scattering, Friedel pairs were merged and the absolute configuration was assigned from the starting material.
The H atoms were all located in a difference map, but those attached to carbon atoms were repositioned geometrically.
The H atoms were initially refined with soft restraints on the bond lengths and angles to regularize their geometry (C-H in the range 0.93-0.98, N-H in the range 0.86-0.89 N-H to 0.86 O-H = 0.82 Å) and U iso (H) (in the range 1.2-1.5 times U eq of the parent atom), after which the positions were refined with riding constraints.
One outlying reflection was omitted from the refinement as it was thought to be partially occluded by the beam stop.